how to write a functions(program) for transmitting and receiving data over uart using nrf 51822?

Question

Hi, there i am using nrf51822 to communicate with quectel ec25 .i want to send AT commands over uart and receive some response from quectel.for eg. i am sending a "AT" command i should get "ok" response in return.i am referring nrf5 sdk10.0.0 uart example and in that example there is loop back test and i have disabled that but i didnt understand the code flow and the functions that are used in this example.what are the changes i have to make in my code to transmit and receive data over uart .This is the example:can somebody explain me which part of code is sending and receiving data.please urgent help needed.and i dont want to use ble _uart example just want to use a simple uart communication.

#include <stdbool.h> #include <stdint.h> #include <stdio.h> #include "app_uart.h" #include "app_error.h" #include "nrf_delay.h" #include "nrf.h" #include "bsp.h"

//#define ENABLE_LOOPBACK_TEST /**< if defined, then this example will be a loopback test, which means that TX should be connected to RX to get data loopback. */

#define MAX_TEST_DATA_BYTES (15U) /< max number of test bytes to be used for tx and rx. */ #define UART_TX_BUF_SIZE 256 /< UART TX buffer size. */ #define UART_RX_BUF_SIZE 1 /**< UART RX buffer size. */

void uart_error_handle(app_uart_evt_t * p_event) { if (p_event->evt_type == APP_UART_COMMUNICATION_ERROR) { APP_ERROR_HANDLER(p_event->data.error_communication); } else if (p_event->evt_type == APP_UART_FIFO_ERROR) { APP_ERROR_HANDLER(p_event->data.error_code); } }

//#ifdef ENABLE_LOOPBACK_TEST /** @brief Function for setting the @ref ERROR_PIN high, and then enter an infinite loop. */ static void show_error(void) {

LEDS_ON(LEDS_MASK);
while(true)
{
    // Do nothing.
}

}

/** @brief Function for testing UART loop back.

@details Transmitts one character at a time to check if the data received from the loopback is same as the transmitted data.
@note @ref TX_PIN_NUMBER must be connected to @ref RX_PIN_NUMBER) */ /*static void uart_loopback_test() { uint8_t * tx_data = (uint8_t *)("\n\rLOOPBACK_TEST\n\r"); uint8_t rx_data;

// Start sending one byte and see if you get the same for (uint32_t i = 0; i < MAX_TEST_DATA_BYTES; i++) { uint32_t err_code; while(app_uart_put(tx_data[i]) != NRF_SUCCESS);
```
nrf_delay_ms(10);
err_code = app_uart_get(&rx_data);

if ((rx_data != tx_data[i]) || (err_code != NRF_SUCCESS))
{
    show_error();
}
```
} return; }

#endif*/

/**

@brief Function for main application entry. */ int main(void) { LEDS_CONFIGURE(LEDS_MASK); LEDS_OFF(LEDS_MASK); uint32_t err_code; const app_uart_comm_params_t comm_params = { RX_PIN_NUMBER, TX_PIN_NUMBER, RTS_PIN_NUMBER, CTS_PIN_NUMBER, APP_UART_FLOW_CONTROL_ENABLED, false, UART_BAUDRATE_BAUDRATE_Baud38400 };

APP_UART_FIFO_INIT(&comm_params, UART_RX_BUF_SIZE, UART_TX_BUF_SIZE, uart_error_handle, APP_IRQ_PRIORITY_LOW, err_code);

APP_ERROR_CHECK(err_code);

//#ifndef ENABLE_LOOPBACK_TEST printf("\n\rStart: \n\r");

while (true)
{
    uint8_t cr;
    while(app_uart_get(&cr) != NRF_SUCCESS);
    while(app_uart_put(cr) != NRF_SUCCESS);

    if (cr == 'q' || cr == 'Q')
    {
        printf(" \n\rExit!\n\r");

        while (true)
        {
            // Do nothing.
        }
    }
}

//#else

// This part of the example is just for testing the loopback .

// while (true) // { // uart_loopback_test(); // } //#endif*/ }

/** @} */ great help appriciated!!